By-product recovery process and apparatus



L. R. FORREST BY-PRODUCT RECOVERY PROCESS AND APPARATUS Filed Oct. 2 1928 3 Sheets-Sheet l INVENTOR 3 MMZM 7 ATTORNEYS Gd. 1% 1933.. L R o R sT LQIMRHZQ BY-PRODUCT RECOVERY PROCESS AND APPARATUS Filed Oct. 24, 1928 SSheet-Sheet 2 g M q i Tfi L! 2 i a v N w INVENTOR i 7; /7M

ATTORNEYS ct. m, E33.

2.. R. FORREST BY-PRODUCT RECOVERY PROCESS AND APPARATUS Filed Oct. 24, 1928 '3 Sheets-Sheet 3 INVENTOR @JM 051% Z; r Mq ATTORNEYS Patented Oct. 10, 1933 UNITED? STATES PATENT OFFICE BY-PRODUCT RECOVERY PROCESS AND APPARATUS Laurence Raymond Forrest, South Orange, N. 3., assignor to The Barrett Company, New York, N. Y., a corporation 01' New Jersey Among the objects of the invention are the simplification of the operation of by-product coke ovens, etc. with a view to the simultaneous production of coal tar pitch, clean tar oils, ammonium sulfate and coke oven light oils under new and improved conditions.

According to the present invention, tar is-collected in collector mains and the tar so collected is distilled in another collector main by direct contact with hot coal distillation gases to give a. pitch residue, while the vapors from the distillation are admixed with and pass ofi with the gases employed for the distillation.

The coal distillation gases from which the tar is separated, and those employed for the distillation of the tar, are subjected to a cleaning operatic-n, as by electrical precipitators, to remove suspended tar and pitch particles therefrom; and the temperature of the gases prior to and during cleaning is so regulated that when the gases are admixed and passed to the ammonia saturator, they will be above the dew point of water.

The present invention provides an improved arrangement of by-product equipment in which a series of collector mains are arranged at successively lower levels, so that tar may 'fiow' by gravity from one to another, and so that tar may flow by gravity from the last collector main to the main employed for tar distillation, thus simplifying the equipment and eliminating much equipment that would otherwise be required. The invention also provides an improved ammonia liquor circulating system, and an improved method of recovering ammonia from the excess liquor of such system;

The nature and advantages of the invention 50 will more fully appear from the following more detailed description, taken in connection with the accompanying drawings, which illustrate, in a somewhat conventional and diagrammatic manner, the improved by-product recovery 55 equipment of the invention, which is adapted for the carrying out of the improved process of the invention.

In the accompanying drawings.

Figs. 1A and 13 together are a plan view showing part of a coke oven block with the by-product recovery equipment of the invention.

Figs. 2A and 2B show the equipment in elevation.

Fig. 3 is an enlarged sectional view, with part in elevation, showing the arrangement of one of the precipitators.

Fig. 4 is an enlarged view showing one of the agitating rolls.

Fig. 5 is an enlarged view showing the connection between the collector main and the distilling to main, parts of the mains being broken away; and

Fig. 6 shows one arrangement of pitch outlet from the distilling main.

Part of a coke oven block is indicated conveni5 tionally at 1. The hot gases from the individual coke ovens pass through the individual uptake pipes 2 into collector mains of which three are shown in the drawings, for purposes of illustration, so that the battery as shown is divided into three sections, each section being served by a separate collector main. Two of these collector mains, indicated at 3 and 4;, are. ordinary mains, while the third main, indicated at 5, is a tar distilling main.

The tar distilling main 5 may be of any desired length, and may have a larger or smaller number of ovens connected thereto to provide an increased or decreased volume of hot coke oven gases for the distillation of tar in the main. In a sixty-oven block, divided equally into three sections of twenty ovens each, servedby separate collector mains, the tar distillation 'main may be connected to a third of the ovens of the block, and each of the ordinary collector mains will similarly be connected to a third of the ovens of the block. The tar distillation main, may, however, be shorter and connected to only a quarter or a fifth or a sixth or less of the ovens of the battery, depending upon the distillation desired and the quality of the pitch desired at the particular coke plant location.

By employing an ordinary collector main for tar distillation, the installation of a special distilling main is avoided, and equipment of the kind commonly employed at coke oven plants can be employed for the distillation.

The two ordinary collector mains 3 and 4 can be operated in the ordinary way, with supply of ammonia liquor, or of liquor and tar,.for flushing the main. The operation of these mains, so far as the supplyv of cooling and flushing liquid is ,concerned, may be the same as is common in the operation of present day collector mains at coke oven plants. In the apparatus illustrated, these -two collector mains are supplied with liquor and tar will flow towards the tar distillation main. The liquor sprayed and flushed into collector main 3, and the tar condensed therein, flow toward and into thev collector main 4 where they combine with the liquor and tar introduced into and condensed in this main.

The combined liquor and tar flow from the main 4 into the decanter 9 in which the liquor separates from the tar. The tar collecting in the bottom part of the decanter flows through a seal into the outlet pipe 10 through which it enters the distilling main 5. In the detail drawings, Fig. 5, the taroverfiow is shown witha hand-controlled gate 9', and an inspection T 10' for the purpose of maintaining control of the decanter operation. Any suitable valve means may be used instead of that shown. The valve'controls the decanter operation, the tar flowing into the tar distillation main as nearly as possible at the rate at which it is produced.

In the tar distilling main 5 the tar is brought into direct and intimate contact with the hot coke oven gases passing therethrough, in order that the heat of the hot coke oven gases may efi'ectively be employed for its distillation. Effective contact can be readily obtained by atomizing or spraying the tar into the hot coke oven gases. In the apparatus illustrated, the atomizing or spraying devices are rapidly rotating rolls 11, each being individually driven by a motor 12. These rolls have their axes at right angles to the axis of the tar distilling main so that, as the rolls are rapidly rotated, the tar will be atomized or sprayed upwardly and longitudinally of the distilling main and brought into intimate contact with the hot coke oven gases passing through the main.

The tar flowing automatically and continuously from the collector mains 3 and 4 into the decanter 9 and then into the distilling main 5 is thus subjected to a spraying action which effects an intimate contact between the tar and the hot gases with the result that it is first dehydrated and then progressively distilled so that the residue from the distillation passes from the opposite end of the distilling main as a pitch product. As the dehydration and distillation progress, the tar will be dehydrated and progressivelydistilled so that the material atomized or sprayed into the hot gases will progressively change in character and will, near the outlet end of the distilling main, be a pitch which, when cooled and solidified, will have a relatively high melting point.

Inasmuch as the tar enters the distilling main continuously and automatically, without preheat is readily supplied, however, by having a sufiicient number of ovens connected to the distilling main. With a sufl'lcient number of ovens so connected, suflicient heat will be supplied in the form of hot coke oven gases to. dehydrate the tar and to distill it to produce pitch of relatively high melting point, e. g., pitch of melting point up to around 400 F.

The distillation. operation can be regulated in the distilling main in various ways, for example, by controlling the cooling of the gases by radiation losses, or by reducing such losses by effective insulation. The distilling operation can also be regulated, where a softer pitch is desired, by reducing the temperature of the gases and their distilling power by spraying or atomizing a limited and regulated quantity of water thru sprays in the uptake pipes, supplied by the line 12, or water may be sprayed into the gas space of the distilling main. Where tar from another source is introduced into the ordinary collector main, it will supplement the tar produced in such main, and the distillation can be regulated to some extent by regulating the amount of additional tar thus supplied. In a self-contained system, however, where only the tar is available for distillation that is produced in the other collector mains, and where all of the tar so collected is subjected to distillation, the regulation is effected otherwise, as by regulating the intimacy of atomizing or spraying, or by a regulated cooling of the gases, etc.

The pitch outlet from the distilling main is shown in Fig. 6 as a spout 13 sealed by the pitch in the main and through which the pitch flows automatically to maintain a predetermined level in the distilling main. By regulating the level in this way, and by adjusting the location of the rapidly rotating spray rolls, these rolls will dip into the tar or pitch to the necessary extent to secure efiective spraying or atomizing of the tar or pitch into the gases. The pitch withdrawn through the outlet 13 may be collected and conveyed to any suitable place of storage or use. As shown, the pitch discharges into a trough 14 and is subjected to water jets supplied through the pipes 15 so that the pitch is suddenly solidified and chilled and broken up into a pulverulent state, in which form it is flushed by the water to a place (not shown) where the pitch is separated from the water.

The ammonia liquor separated from the tar in the decanter 9 overflows through the side over-flow and inspection T 16 and is pumped by the pump 17 through the line 18 to supply the ammonia liquor for the sprays 6. The liquor is thus recirculated through the two collector mains 3 and 4. The circulating liquor will gradually build up in strength of fixed ammonia, and, for this reason, as well as because of the evaporation taking place in the ordinary mains, fresh water will be added to the circulation in small and regulated amounts. The inlet for such fresh water is indicated at 19. To maintain the liquor circulation at aconstant strength, in respect of fixed ammonia, e. g. a strength of 20 to 30 grams per liter, a continuous withdrawal of ,liquor from the circulating system is made through the pipe 20. 1

Each of the three collector mains is equipped with an electrical precipitator. The gases from the ordinary collector mains 3 and 4 enter their respective precipitators 21 and 22 at a lower temperature than the gases from the distilling main 5 enter the precipitator 23. The gases from the mains 3 and 4, entering the precipitators 21 and 22, may, however, be at a higher temperature than the normal gas outlet temperature from such mains, this temperature being controlled by the quantity of spraying liquor and the intimacy of spraying of such liquor into the gases in the mains.

The gases from the ordinary mains, after passing through the precipitators, combine with each other and the combined gases in "turn combine with the hot gases from the precipitator 23 on the distilling main to give a gaseous mixture of higher temperature than the gases coming from the.precip itators 21 and 22 but at a lower temperature than the gases coming from the precipitator 23. The combined gases, at a regulated temperature, are then passed to the ammonia saturator, as hereinafterdescribed. A butterfly valve connected with a pressure regulator 23' is shown in the outlet from each precipitator to control the flow of gas from each of the mains.

It is desirable to produce a hot gas stream from the combined three precipitators which is unsaturated with water vapor to the maximum extent possible. In order to avoid vaporizing an excess of liquor in the ordinary mains 3 and 4, the sprays in these mains are so designed and located that little if any liquor spray passes down through the gas space. As illustrated in Fig. 3, the sprays are fan-shaped and are located at the top corners of the mains and point in a direction tangential to the side surfaces. This methodof washing prevents the accumulation of pitch on the main surface and avoids intimate contact of the liquor with the gas.

The electrical precipitators 21 and 22 on the ordi .ary distilling mains 3 and 4 will separate from the gases the suspended particles of pitch and tar, so that the gases leaving the precipitators will be substantially tar-free gases. The separated tar or ,pitch will flow back into the collector mains and will there blend with the current of liquor and tar flowing through the mains. The character of the tar or pitch so precipitated will depend upon the temperature of the gas leaving these precipitators.

The precipitators are shown as provided with heating or cooling jackets by means of which a temperature regulating medium can be circulated therethrough. The temperature will be so controlled that the precipitates from the precipitators 21 and 22 will have a melting point sumcien tly low so that it will readily blend with the current of liquor and tar flowing to the bottom of the main. It may have a melting point, for

example, well below F.

, In order to assure the flow of the precipitated tar or pitch in the proper direction, liquor jets 45 and 46 may be located at the bottom of the main beneath the precipitators and pointing towards the discharge end of the main. The precipitated tar or pitch will thus blend with the liquor and tar and be carried therewith into the decanter, where the liquor will be separated, and the composite tar will then flow to the distilling mam.

' The electrical precipitator 23 on the distilling main will also clean the gases and vapors passing therethrough from suspended pitch particles, which pitch will flow back into the distilling main and there blend with the pitch undergoing distillation therein. The resulting cleaned gases, carrying a considerable amount of oil vapors therein, mix and blend with the gases from the other precipitators to form a composite gasmixture which passes through the gas line 24 to the ammonia saturator.

The admixing of the hot enriched gases from the distilling main with the cooler gases from the ordinary mains will bring about some condensation of heavy oils from the admixed gases, and further cooling and condensation of the gaseous mixture may take place before the gases reach the ammonia saturator. A trap 25 is arranged in the gas main 24, as close to the saturator as possible, for collecting condensed oils which are drawn off through the drip leg 26.

The temperature of the admixed gases is regulated and controlled, so that, after allowing for radiation loss in the connecting lines, the gases will enter the saturator at a temperature above the dew point of water, e. g. the gases may enter the saturator at a temperature around 100 C. or higher. The ammonia contained in the gases 95 will combine with the sulfuric acid in the saturator to form ammonia sulfate. The saturator 27 is shown as having the usual ejector 39 and flush box 40 with drain returning to the saturator. The centrifugal separator 41 completes the separation of liquor from the ammonium sulfate crystals.

The saturator is insulated to keep oil condensation at a minimum. The agitation of the sat- ,urator bath may be sufliciently violent to cause 103 oil, which separates in the saturator, due to condensation or removal of entrained droplets of oil from the gases, to be delivered to the flush box 40. On centrifuging the ammonium sulfate,

all but an inappreciable amount of such oil as is 1.10 delivered to the'centrifuge will be returned to the saturator with the separated liquor.

Fig. 2B shows means for withdrawing small batches of mother liquor from the saturator to a small decanter 41 for separating such oil as may condense and separate in the saturator. By periodic removal of small batches of mother liquor from the saturator to the decanter, and return of the mother liquor to the saturator system thru the flush box 40, after decanting oil therefrom, the accumulation of oil in the saturator system can be prevented without any interruption in the operation of the saturator.

The excess liquor from the ammonia liquor circulating system, after it has been built up to say 20 to 30 grams per liter of fixed ammonia, is also passed directly to the sulfate saturator. The arrangement is such, however, that this liquor is first admixed with the .acid supplied to the saturator so that any free ammonia contained in the circulating liquor will be first combined with the acid. The admixed acid and liquor is then introduced into the saturator through a combined gas saturator and acid separator where the mixture is brought into intimate contact with the gas leaving the sulfate saturator. This gas saturator is indicated at 29 and may be in the form of a small tower having filling material adapted to bring the liquor and gas into intimate contact with each other. V

In the apparatus illustrated, the acid supply line 36 and the excess liquor line 20 combine and enter the preheater 37, where the mixed acid and liquor are preheated to a regulated temperature, and the preheated mixture is then discharged into the top of the acid separator, through spray nozzles 38. The gases from the sulfate saturator rise through -the gas pipe 28 to the bottom of 'the acid separator, and the gases from the top of the separator escape through the pipe 30.

The gas leaving the sulfate saturator is not saturated with water vapor at the particular temperature of the bath, due to the reduced vapor tension of the saturated mother liquor. This gas is therefore capable of vaporizing additional liquor. The preheating of the excess liquor and acid before their introduction into the gas saturator and acid separator, combined with the heating and vaporizing effect of the gases leaving the saturator, results in a partial vaporization of the excess water. The hot gases entering the saturator through the gas line 24 are also at a temperature such that they assist in this vaporization of excess water. By the combined heating and vaporizing actions which take place in the sulfate saturator 2'! and in the gas saturator 29, and with the heat supplied by the preheater 37, the excess water introduced with the liquor from the line 20 can readily be removed.

I do not claim herein the particular construction and operation of the ammonia saturator 27 with the gas saturator 29, inasmuch as this is the invention of W. B. Wingert as set forth in application Serial No. 334,753, which was filed January 24, 1929 and which has matured into U. S. Patent No. 1,880,631; but I claim herein, as part of the present invention, the combination of this type of saturator with the by-product recovery system in which the hot admixed gases in a tar-free state pass directly to the saturator and in which the excess ammonia liquor is also passed directly to the saturator.

The gasses leaving the saturators pass through the pipe 30 to the final cooler 31 which may be a single stage or multi-stage cooler, made up of one or more units, of which one is shown. Cooling is effected by fresh water sprayed into the top of the cooler, and the oil and water mixture withdrawn from the bottom is passed to a decanter or separator 33 from which the water and oil are separately withdrawn through lines 34 and 35. The gases from the final cooler pass to the exhauster 32 and thence to a light oil recovery system (not shown).

The improved process and apparatus of the present invention present many advantages. Much of the equipment now commonly provided in coke oven by-product recovery systems is eliminated or greatly simplified. By locating the decanter for separating the tar and ammonia liquor on top of the block, the handling of tar as such is avoided, the tar fiowing automatically without pumping from the ordinary collector mains to the distilling main. Tar is thus handled only in the form of its finished products, namely, hard or soft pitch and clear tar oils. The ammonia liquor circulating system is also greatly simplified. The condensing system is also simplified and much of the present apparatus and piping is eliminated. The distillation main takes the place of an ordinary collector main, thus eliminating added equipment for distillation.

The present invention presents the further advantage, among others, that the need of a separate ammonia still for the release of fixed ammonia is eliminated, and the fixed ammonia is directly recovered in the saturator with utilization of the heat of the hot gases for distilling excess water from the liquor. The ammonium sulfate is moreover obtained in a substantially tarfree state; while the gases and oils recovered from the gases will also be free or substantially free from tar. The elimination of tar from the gases entering the light oil scrubbers will eliminate.

the sludge deposit which normally forms on the grids of the light oil recovery scrubbers,

thus reducing the cleaning operation required on such scrubbers.

The invention, moreover, can be applied to existing coke oven plants, employing the ordi-. nary uptake pipes and. collector mains, excep t for the location of the ordinary mains somewhat higher than the tar distillation mains with corresponding change in the length of the uptake pipes, and. with substitution for the ordinary cross-over mains and tar and ammonia liquor collecting systems of the much simpler gas cleaning and handling equipment and decanter arrangement and liquor circulating system of the present invention.

I claim:

1. In the operation of by-product recovery systems of coal distillation plants, the steps which comprise cooling parts of the coal distillation gases and separating tar therefrom, cleaning the resulting gases to separate suspended tar and pitch particles therefrom, distilling-tar by bringing it into intimate contact with another part of the hot coal distillation gases, cleaning the resulting gases to separate suspended tar and pitch particles therefrom, and combining the cleaned gases from which the tar has been separated and the cleaned gases employed for the distillation at a temperature above the dew-point of the gases for water before passing the gases through an ammonia saturator and passing the combined gases to an ammonia saturator at a temperature above the dew-point of Water.

2. The process according to claim 1 in which heavier oils distilled from the tar are condensed and separated from the mixed gases before they pass to the ammonia saturator.

3. The process according to claim 1 in which the tar separated from part of the coal distillation gases is automatically and continuous1y'sup-- plied for distillation by another part of such gases.

4. The process according to claim 1 in which the tar and pitch separated on cleaning of the respective gases are combined with or admixed with the tar previously separated from the gases and the pitch resulting from the distillation by the gases respectively.

5. In the operation of the by-product recovery system of a coal distillation plant the steps which comprise cooling the coal distillation gases from one part of the plant to separate tar therefrom, continuously removing the tar from said gases and causing it to fiow in a continuous which comprise collecting the gases from a num-.. ber of coal distillation ovens or retorts ir 1 at.

least one collector main and separating tarfrom the gases in such main or mains, drawing off the resulting tar and permitting it to flow by gravity into another collector main, collecting hot coal distillation gases from a plurality of ovens or retorts in said other collector main and bringing the tar into intimate contact with such gases at a temperature sufficient to eiiect distillation of the tar and the production of a pitch residue.

7. In the operation of by-product recovery systems of coal distillation plants the steps which comprise collecting hot coal distillation gases from a number of ovens or retorts in at least one collector main, introducing ammonia liquor into such main or mains and separating tar from the gases therein, drawing ofi the resulting liquor and tar and separating the liquor from the tar, supplying the resulting tar automatically and by gravity to another collector main, collecting hot coal distillation gases in said other main at a temperature suificient to effect distillation of the tar and bringing the tar into intimate contact therewith to effect such distillation.

8. In the operation of by-product recovery systerns of coal distillation plants the steps which comprise collecting gases from a number of coal distillation ovens or retorts in at least one collector main, supplying ammonia liquor to such main or mains and withdrawing ammonia liquor and tar therefrom, liquor and tar and recirculating the ammonia liquor, withdrawing part of the ammonia liquor after it has increased in content of fixed ammonia and conveying such liquor to the sulfate saturator, cleaning the coal distillation gases to remove suspended tar and pitch particles therefrom, and passing the cleaned gases to the sulfate saturator at a temperature sufficiently above the dew-point of water to eifect distillation of water from fixed ammonia liquor added to the saturator.

9. The further improvement in the process of claim 8 in which the fixed ammonia liquor is admixed with acid and supplied to the saturator as a preheated mixture.

10. In the operation of by-product recovery systems of coal distillation plants, the steps which comprise collecting hot coal distillation gases from a number of ovens or retorts in at least one collector maini and separating tar from such gases therein. introducing ammonia liquor into such main or mains and withdrawing ammonia liquor and tar therefrom, separating the ammonia liquor and tar, recirculating the ammonia liquor through the main or mains with addition of fresh water, withdrawing the excess of ammonia liquor high in fixed ammonia and passing the same to the sulfate saturator, distilling the tar by direct contact with hot coal distillation, gases from other ovens or retorts to give a pitch residue and gases enriched in oil vapors, cleaning the resulting gases to separate suspended pitch particles therefrom, cleaning the coal distillation gases from which the tar has been separated to remove suspended tar and pitch particles therefrom, combining the clean gases and passing the resulting gas and vapor mixture to the sulfate saturator at a temperature above the dew-point of water.

11. The further improvement in the process of claim 10 in which the ammonia liquor rich in fixed ammonia is admixed with acid and supplied to the saturator in the form of a pre-heated mixture, and in which such mixture is separating the ammonia production of pitch therefrom, means for cooltherein, a distillation main connected to a plurality of coal distillation ovens or retorts, means for supplying to such main by gravity and in an automatic manner the tar separated from the ases in said first-mentioned mains and means in the main for bringing the tar into intimate contact with the gases to effect distillation thereof and to produce a pitch residue.

13. A by-product recovery system for coaldistillation plants comprising a plurality of collector mains, one of said mains being a tar distilling main and the other main or mains being tar separating and collecting mains, means for supplying automatically by gravity to the tar distillation main the tar collected in the other mains, and means in the tar distillation main for bringing the tar into intimate contact with the hot coal distillation gases therein to effect distillation of the tar.-

14. A by-product recovery system for coal distillation plants comprising a block of coal distillation ovens or retorts having a plurality of collector mains each connected with a number of ovens or retorts through individual uptake pipes, one of said mains being a tar distillation main with means for bringing tar into intimate contact with the hot gases passing therethrough to effect distillation of the tar, the other main or mains being tar'collecting mains having means for introducing cooling liquid therein to cool the gases and flush the mains, means for drawing ofi the tar collected in said mains and for supplying it automatically by gravity to the tar distillation main.

15. A by-product recovery system for coal distillation plants comprising a block of coal distillation ovens or retorts having a plurality of collector mains each connected to a number of the ovens or retorts through individual uptake pipes, one of said mains being a tar distillation main having means for bringing tar thereininto intimate'contact with the hot coal distillation gases passing therethrough to effect distillation of the tar and the production of pitch therefrom, the other main or mains having means for introducing ammonia liquor therein and for withdrawing ammonia liquor and tar therefrom, a decanter arranged to receive the tar and ammonia liquor so withdrawn, said decanter being arranged to permit the tar to flow therefrom by gravity into the tar distillation main, and means for recirculating the ammonia liquor from the decanter to the mains.

16. A by-product recovery system for coal distillation plants comprising a plurality of collector mains each connected to a number of ovens or retorts, means for bringing tar into intimate contact with the gases in one of said mains to effect distillation of the tar and the ing the gases in the other main or mains to separate tar therefrom, means for cleaning the gases from said mains to separate suspended tar and pitch particles therefrom, and means for 50 combining the gases from said mains to give a gaseous mixture at a temperature above the dewpoint of water and for passing such gases at such temperature to a sulfate saturator.

17. A by-product recovery system for coal distillation plants comprising a plurality of collector mains each connected to a number of the ovens or retorts of the plant, one of which is a tar distillation main, the balance being cooling mains, electrical precipitators equivalent in number to the number of mains, means for cooling the gases in the cooling mains to separate tar therefrom, means for passing the gases from each cooling main to a precipitator and returning tar and pitch from the precipitator to admix with the tar in said mains, automatic means for supplying tar withdrawn from the cooling mains to the tar distillation main and for bringing it therein into intimate contact with hot coal distillation ,gases to effect distillation of the tar, means for passing gases from the distillation main to the other precipitator and for returning pitch from the precipitator to the main, and means for combining the cleaned gases from such precipitators and for cooling the same to separate clean oils therefrom.

18. Apparatus comprising a plurality of collector mainseach connected to a number of ovens or retorts, one of which is a tar distillation main, the balance being cooling mains, electrical precipitators equal in number to the number of mains for removing suspended tar and pitch particles from the gases leaving the respective mains, a decanter for separating tar and ammonia liquor, means for introducing ammonia liquor into each of said cooling mains and means for withdrawing tar and ammonia liquor therefrom to the decanter, circulating means for circulating ammonia liquor from the decanter to the means for introducing it to the mains, means for supplying fresh water to the circulating ammonia liquor and for withdrawing the excess liquor rich in fixed ammonia and passing the same to a sulfate saturator, the tar distillation main being so arranged that the tar from the decanter will enter the same by gravity, means in said distillation main for bringing the tar into intimate contact with the gases passing therethrough to effect distillation of the tar and the production of pitch therefrom, means for combining the hotter gases and the'precipitator connected with the distillation main, with the cleaned gases from the other precipitators and for passing the cleaned gases to the sulfate saturator at a temperature above the dew-point of water.

LAURENCE RAYMOND FORREST. 

